<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <label>To-Do List</label>
  <ol contenteditable><li></li></ol>
  <script>
    var area = document.querySelector('ol');
    area.innerHTML = sessionStorage.getItem('todo') || '<li></li>';
    area.addEventListener('input', function() {
      sessionStorage.setItem('todo', area.innerHTML);
    });
  </script>
</body>
</html>
